Most plastics used for engineering purposes have a limit. When exposed to high levels of heat, stress, and even chemicals, their effectiveness rapidly declines. But not PEEK. Polyether ether ketone (PEEK) is in a class all by itself when it comes to engineering thermoplastics.
It resists softening or breaking nylon, Delrin, or even PTFE at temperatures that would cause them to soften or break. It is resistant to aggressive chemicals and heavy mechanical loads and can be sterilized repeatedly without breaking down. If medical device engineers, aerospace designers, and semiconductor equipment manufacturers are all turning to the same plastic, it’s time to pay it some attention.
This blog post describes what PEEK is, why it’s so capable when compared to other plastics, its various applications, its machining process, and its performance compared to its closest competitors.
What Is PEEK Plastic?
PEEK is an acronym for Polyether Ether Ketone. It is a semi-crystalline thermoplastic polymer of the PAEK (Polyaryl Ether Ketone) family, which has an aromatic backbone structure providing outstanding thermal stability.
Designed in 1978 by ICI Chemicals, the material is now the industry standard high performance engineering plastic for challenging industries. Its molecular structure contains repeating ether and ketone linkages around the benzene rings, which give it a polymer with the properties of being rigid, chemically inert, dimensionally stable, and resistant to thermal environments that would destroy traditional plastics.
There are various grades of PEEK material for use:
Unfilled (virgin) PEEK — baseline mechanical and chemical performance, preferred for medical and food contact applications.
Carbon fiber-reinforced PEEK—much higher stiffness and strength, low thermal expansion
Glass fiber-reinforced PEEK — rigid, extremely dimensionally stable under load.
PEEK-HPV (bearing grade) combined with carbon fibre, graphite, and PTFE for dry-running tribological applications
Medical grade PEEK— is biocompatible, implantable, ISO 10993, and USP Class VI approved.
Goals are defined by grade-level performance levels. The choice of a suitable material is very important, and virgin PEEK in a bearing application will wear out much sooner than bearing-grade PEEK, which is specifically designed as a bearing.
Key Material Properties That Set PEEK Apart
PEEK is a highly advantageous material for a variety of reasons, including its key material properties. To understand the advantages of PEEK, one needs an appreciation of the actual figures and not just the words.
Thermal performance
The first application to justify the high cost of PEEK is its thermal performance. The continuous service temperature is 250°C, and the short-term service temperature is 300°C. The glass transition temperature (Tg) is around 143°C, and the melting point is around 343°C. To give some perspective, nylon 66 softens at about 180°C, and POM (Delrin) loses structural integrity at 90-100°C when it is loaded continuously.
Mechanical strength
Mechanical strength is retained under high temperatures. Unfilled PEEK’s tensile strength is 100 MPa, and flexural modulus is 3.6 GPa at room temperature, which are decently high for such a high-temperature polymer.
Thermal expansion
Thermal expansion is very crucial for precision parts. Unfilled PEEK maintains its size and shape more precisely than most plastics because it expands very slowly at different temperatures. It helps parts fit properly and preserve tight clearances even when working in hot environments.
Radiation resistance
Radiation resistance allows for the use of PEEK in applications such as nuclear and medical imaging applications, where most polymers deteriorate quickly.
Biocompatibility
The biocompatibility, especially of the medical-grade PEEK, enables implantable applications. Radiolucent, meaning that it will not cause any artifact interference during imaging following surgery. It has been used in many worldwide applications for spinal, orthopedic, and dental implants due to this single property.
The Use of PEEK in Industrial Applications:
The properties of PEEK can be very wide ranging, and each specific application makes use of a particular combination of these properties.
Aerospace and Defense
In the aerospace field, these constraints are weight, temperature, and dimensional precision. Where weight is a concern and temperatures rise beyond what conventional engineering plastics can withstand, PEEK components are used in bracket systems, bearing cages, bushings, and structural inserts in place of aluminum and titanium.
Aircraft uses the flame resistance and low smoke emission of cable and wire insulation. Another natural application is fuel system components that come into contact with aggressive fluids at high temperatures.
Medical Devices & Implants
Medical grade PEEK is essential for orthopedic surgery. Many spinal fusion cages, bone screws, and trauma fixation devices are now being produced using PEEK instead of titanium—principally because the modulus of elasticity of PEEK is closer to that of cortical bone than metals, which means there is less stress shielding and the possibility of bone resorption over time.
PEEK is not only used for implants but also for surgical instrument handles, endoscope components, sterilization trays, and drug delivery mechanisms.
Semiconductor and Electronics Manufacturing
Cleaning and processing semiconductor and electronics parts. Cleaning and processing semiconductor and electronics parts. Process equipment in semiconductor manufacturing should be capable of withstanding high purity, plasma, and aggressive chemical etchants.
PEEK is used in wet process equipment parts such as wafer handling parts, pump housings, valve seats, and fasteners where its minimal particle generation and chemical inertness are the most important attributes.
Oil and Gas
The high temperatures, pressures, and corrosive chemical activity found in downhole drilling environments can cause traditional materials to deteriorate rapidly. Where alternatives fail, PEEK seals, valve components, and cable insulation survive.
Industrial Machinery and Bearings
Where oil contamination is an issue, bearing-grade PEEK can operate without lubrication, such as in food processing equipment, clean rooms, and medical machinery. It can be used under dry running conditions because of its low coefficient of friction and high wear resistance, which can be not achieved by metals without lubrication systems.
Machining PEEK: Critical Considerations
PEEK machines that is comparable to many other high-performance polymers, but must be respected. The two properties that determine the approach to machining are low thermal expansion and sensitivity to cutting heat.
However, PEEK’s CTE is much lower than that of most polymers, so it will not tolerate dimensional changes due to thermal distortion as well as softer materials. Controlled cutting conditions are the only way to obtain tight tolerances, not after heat induced distortion.
The risk of heat build-up is the main one when machining. Excessive cutting temperatures can locally melt the resin matrix, resulting in surface degradation, dimensional drift, and poor finish. There are strategies to help control this:
- Always use sharp carbide tooling—dull tools create friction heat, not clean cutting action
- Use positive rake angles to reduce cutting forces.
- Use a continuous supply of coolant or compressed air, especially where it is necessary to make deep cuts and in confined pockets.
- Don’t exceed conservative feed rates and depths of cut, particularly for features that are thin or small.
- Wait for parts to get to thermal equilibrium before the final dimensional check.
Reinforced grades, especially PEEK filled with carbon fiber, can cause tooling wear. High volume production settings will benefit from long life with diamond coating tools or PCD (polycrystalline diamond) tooling.
Experienced precision CNC plastic machining companies are familiar with dealing with such limitations. The surface finish, dimensioning, and scrap rates are different between a shop that continuously machines PEEK and one that sees PEEK for the first time.
PEEK vs. Other High-Performance Materials: How It Compares
PEEK vs. PTFE
| Property | PEEK | PTFE |
| Max continuous service temp | 250°C | 260°C |
| Tensile strength | ~100 MPa | ~20–35 MPa |
| Compressive strength | ~138 MPa | ~12 MPa |
| Wear resistance | Excellent | Moderate |
| Chemical resistance | Very broad | Exceptionally broad |
| Machinability | Good | Good (but soft/creep-prone) |
| Cost | High | Moderate |
PTFE is more resistant to a variety of chemicals, as it’s almost impervious to nearly everything except molten alkali metals and fluorine gas. However, PTFE is not mechanically strong. It is subject to creep under load, is not able to support structural loading, and wears relatively quickly in dynamic applications. PEEK performs better than PTFE in all mechanical properties and has good but slightly weaker chemical resistance.
PTFE is valid for seals and gaskets in pure chemical containment. For applications that demand structural integrity, wear resistance, or dimensional precision under load, PEEK is a good choice.
Common Problems and Solutions while Working with PEEK Material
Residual stresses in extruded rods or plates can cause dimensional inaccuracy in PEEK parts. To minimize this, use stress relieved or annealed PEEK material, leave rough-machined parts to rest, and machine to final dimensions after annealing.
Surface cracking or crazing is typically caused by solvents or coolants that are incompatible. Do not use ketone-based and chlorinated cleaners; isopropyl alcohol is safe for cleaning.
Premature wear in bearing applications is caused by the use of virgin PEEK in high friction applications. Use bearing grade PEEK (PEEK-HPV or filled PEEK compounds) for improved wear properties.
Inconsistent tolerances in small features are mainly caused by heat buildup during machining. Limit feeding rates, control coolant flow, and peck holes for deep holes to maintain accuracy.
What Are the Expert Tips for Specifying PEEK Components?
You must be sure to indicate the grade and do so with more than just “PEEK,” since virgin, filled, and medical grade PEEK have different properties and costs. If used for implantable medical use, check for ISO 10993 biocompatibility documentation from your material supplier.
When designing high-temperature assemblies, consider the CTE contrast between PEEK and metal mating parts to avoid binding or gaps between parts over the operating range.
In structural applications, PEEK with 30% CF has a tensile strength of ~200 MPa and has a significantly lower CTE, but has no biocompatibility and has higher tool wear during machining. Ask for material certification and traceability documents—regulated industries (AS9100 and ISO 13485) will require it.
Conclusion
PEEK is not a material you choose because it is convenient or cost-effective. You specify it because the application needs performance that nothing cheaper can reliably deliver—in operating temperature, chemical surroundings, dimensional stability, or biocompatibility.
If PEEK is the correct material to use, the difference between a precision part and a scrap part lies in how it is manufactured—through heat control, proper tooling, and stress management. It is as crucial as the specification of the material that the precision machining partner possesses experience and knowledge of the properties of the engineering plastics.
Looking for precision-machined PEEK parts for medical, aerospace, or industrial uses? For engineering plastic parts that perform in the most demanding situations, FST Metals offers tight tolerances, clean surface finishes, and reliable lead times. Contact us for your instant quote.
FAQ
Why is PEEK an ideal engineering-grade material?
PEEK’s properties include a high continuous service temperature (250°C), excellent mechanical strength at high temperatures, high resistance to a wide range of chemicals, a low coefficient of thermal expansion, inherent flame-resistant properties, and medical-grade biocompatibility. However, no other single polymer can be as good in all directions, hence the market niche of PEEK, which is not cheap.
What do you think of the common industrial applications of PEEK plastic?
PEEK is employed in medical and spine implants, structural inserts, and bearing cages for aerospace applications, wet process equipment for semiconductors, oil and gas downhole seals and valve components, food and pharmaceutical processing bearing components, surgical instruments, and any other application where conventional engineering plastics cannot handle the operating environment.
What are the performance characteristics of PEEK vs. PTFE?
The PTFE is chemically very resistant and has a slightly higher temperature limit, but it is mechanically weak, creeping under constant load and wearing out quickly under dynamic loading conditions. PEEK is significantly stronger, stiffer, and less susceptible to wear. PTFE is still relevant in the field of chemical containment. PEEK demonstrates much superior performance to PTFE in any application calling for structural performance, dimensional precision under load, or wear resistance.
